Manual reset thermostat

ABSTRACT

A trip-free manual reset thermostat wherein the travel of the reset device is limited so that the disc cannot be moved all the way to its reset position of stability. The reset device engages one side of the cantilever mounted flexible switch arm. Such switch arm is formed with an offset so that the disc-operated bumper engages the switch arm at a point spaced from the line of action of the reset bumper. When reset is attempted while the disc remains at temperatures outside the reset temperature range, the reset device and the disc-operated bumper produce a force couple which tends to maintain the switch in the operated condition.

United States Patent [72] Inventor Anton J. Gerich 3,317,693 5/1967 Bolesky 337/335 Mansfield, Ohio 3,219,783 11/1965 Odson 337/354 X [21] Appl. No. 7,896 3,164,702 1/1965 Ruckriegel et al 337/346 Ex i Primary Examiner-Bernard A. Gilheany Assistant Examiner-Dewitt M. Morgan [73] Ass'gnee Incorporated Anome McNenn Farrin ton Pearne and Gordon Mansfield, Ohio y a g a 54] MANUAL RESET THERMOSTAT 8 claims, 5 Drawing 8g ABSTRACT: A trlp-free manual reset thermostat wherein the travel of the reset device 18 limited so that the dlsc cannot be [52] US. Cl 337/348, moved all the way to i reset i i of ability The reset 337/91337/346337/367 device engages one side of the cantilever mounted flexible [51] Int. Cl ..H0lh 37/70 switch Such switch arm i formed with an offset so that [50] Field of Search 337/91, the disooperaled bumper engages u switch arm at a point 3351 346, 354v 367, 391 spaced from the line of action of the reset bumper. When reset is attempted while the disc remains at temperatures outside [56] Reerences Cited the reset temperature range, the reset device and the disc- UNITED STATES PATENTS operated bumper produce a force couple which tends to main- 3,525,968 8/1970 Hire 337/354 X tain the switch in the operated condition.

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I I n /g MANUAL RESET THERMOSTAT BACKGROUND OF THE INVENTION This invention relates generally to snap-acting thermostats and more particularly to a novel and improved trip-free manual reset thermostat.

PRIOR ART Various types of trip-free manual reset thermostats are known. Examples of such thermostats are illustrated in the U.S.'Pat. to Odsen, No. 3,219,783, the U.S. Pat. to Ruckriegel et al., No. 3,164,702, and the U.S. Pat. to Manecke, Nos. 3,272,946 and 3,428,932. All of these patents disclose bimetallic snap disc thermostats having means for manually resetting the thermostat after it is operated. Also, each of these thermostats is disclosed as trip-free in that the holding of the reset means in its fully operated position does not move the switch to its reset position.

In the thermostat described in the Odsen patent, the body is provided with a fulcrum engageable with a cantilever spring arm and the force of the reset means is applied to the spring arm at a location, spaced from such fulcrum, selected so that the switch is held open when the reset means is fully operated. In the Ruckriegel patent, means are provided to limit the travel of the reset means to an amount which does not cause closure of the switch. The available travel, however, is indicated as sufficient to cause the disc to snap through to its reset position if the temperature of the disc has reached a temperature within a reset range of temperature different from the principal operating temperature. The two Manecke patents disclose a thermostat in which the reset means directly engages the disc and presses the disc toward the reset position. Manecke asserts that his thermostat is arranged so that the switch cannot be closed if the temperature of the disc remains above a predetermined reset temperature.

SUMMARY OF INVENTION The present invention provides a novel and improved tripfree reset system. The reset itself is provided with limited travel arranged so that the reset is capable of moving the disc past a position of instability, but not all of the way to the reset position. With this structure the disc will snap back to the reset position only when its temperature is within a predetermined reset range of temperatures. However, when the disc remains within a range of temperatures within which reset is not desired, the disc holds the contact arm against the reset and retains the switch in the operated condition.

The present invention further provides a structure wherein the reset and the disc apply a force couple to the contact arm when the disc holds the contact arm against the reset. This force couple is arranged to insure that the switch is maintained in the operated position and eliminates the need to maintain extremely close tolerances during the manufacture of the parts to insure proper operation.

In the illustrated embodiment the thermostat is provided with a fixed contact and a mobile contact carried by a flexible cantilever mounted arm. The bumper extends between the mobile contact arm and the disc and is proportioned to move the arm from the closed or reset position to the open or operated position when the disc snaps from its reset position of stability to its operated position of stability.

A reset bumper is provided to engage the side of the mobile contact arm opposite the bumper and causes the disc to move from its operated position of stability past the adjacent position of instability when the reset is operated. The travel of the reset mechanism is limited however, so that the reset cannot be used to push the disc all the way to its reset position of stability. Therefore, the disc will only snap through to its reset position of stability if its temperature is within the range of temperatures in which reset can occur.

The travel of the reset mechanism is also selected so that the switch remains in an operated position even when the reset is depressed. Further, the bumper and the reset are arranged so that the lines of action of the forces they apply to the mobile contact arm are longitudinally spaced from each other and result in a force couple tending to maintain the switch in the operated position whenever reset is attempted while the disc is not within a reset range of temperatures.

In the illustrated embodiments the force couple is insured by providing an offset in the mobile contact arm which insures that the line of force of the bumper is laterally spaced from the centerline of the device.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevation illustrating the exterior of a thermostat incorporating this invention;

FIG. 2 is a longitudinal section of the thermostat illustrated in FIG. 1 illustrating the thermostat in a reset condition prior to operation;

FIG. 2a is a section taken along 2a-2a of FIG. 2 with the bumper removed for purposes of illustration;

FIG. 3 is a section similar to FIG. 2 illustrating the position the elements assume after operation of the thermostat; and

FIG. 4 is a section similar to FIGS. 2 and 3 illustrating the position of the elements when reset is attempted before the disc reaches the reset range of temperatures.

The illustrated embodiment of this invention is a thermostat arranged so that the switch is closed when the disc is in the reset position and is opened when the disc moves to the operating position. The thermostat includes a body assembly 10 consisting of a main body member 11 and a cap member 12, both of which are preferably molded of a plastic material such as phenolic resin or the like. The members 11 and 12 cooperate to define a switch cavity 13. A bimetallic snap disc 14 is positioned against the cap member 12 by a disc-retaining cup 16. Radial location of the disc is provided by a circular wall 17 formed in the cap member 12 and axial location is provided by opposed surfaces 18 and 19 provided in the cap member 12 and disc-retaining cup 16, respectively.

The switch includes a stationary contact 21 which is mounted on the main body member 11 by a rivet 22 which also provides an electrical connection with a terminal member 20. A mobile contact 23 is mounted on the free end of a mobile contact support arm 24 formed of a spring material for movement into and out of engagement with the fixed contact. The mobile contact support arm 24 is secured to the main body member 11 by a rivet 26 which also provides an electrical connection with a terminal 27. The mobile contact arm 24 provides a free arm portion 28 extending from a reverse bend 29 to the free end on which the mobile contact 23 is mounted. In the illustrated embodiment the various elements are arranged so that the two rivets 22 and 26 are located on opposite sides of the free arm portion 28 and so that the free arm portion 28 has a length approaching the diameter of the switch cavity 13. This general type of configuration is illustrated in the US. Pat. to Bolesky, No. 3,317,693 and is particularly desirable for use in thermostats having a relatively small diameter.

A bumper 31 extends through a guide opening 32a formed in the cap member 12 and is engageable at one end with the disc 14 and at its other end with the mobile contact arm 24. The bumper 31 is located on the centerline 32 of the thermostat and is movable by the disc along such line. When the disc is in the reset position of stability, illustrated in FIG. 2, the mobile contact 23 engages the stationary contact 21 and a slight clearance 33 is provided between the ends of the bumper 31 and either the mobile contact arm 24 or the disc 14. The location of the clearance depends upon the mounting position of the thermostat since gravity usually tends to hold the bumper against either the disc or the mobile contact arm. When the disc reaches its operating temperature it snaps through from the reset position of FIG. 2 to the operated position of FIG. 3 and the switch is opened.

Since the thermostat is a manual resettype thermostat, the disc is of a type which does not snap back to the reset position of FIG. 2 under normal environmental temperature conditions. This is accomplished by providing a disc with a wide differential temperature so that once the disc has operated, it tends to remain in the operated position until it is manually reset. It should be understood that such manual reset thermostats may be used in many different types of devices and that in some instances, they are arranged to operate on temperature rise and other instances, they operate when the temperature falls.

In many instances it is desirable to arrange the thermostat so that it cannot be reset until the disc reaches a temperature which is substantially different than the main operating temperature. For example, if the thermostat is used as a safety limit control to shut off an associated device when an excessive temperature is reached, it is sometimes desirable to arrange the thermostat so that it cannot be reset until the temperature of the device drops down a substantial amount into its normal temperature range or reset temperature range.

In such a system the thermostat reset may be arranged to be incapable of moving the disc all the way to its reset position of stability. When the reset travel is limited in this way the disc snaps on through to its reset position of stability only when the disc temperature is within a reset range different than the operating temperature and remains against the reset mechanism when the disc temperature approaches the operating temperature.

In the illustrated thermostat, means are provided for manually resetting the thermostat only when the thermostat is in such a reset range. These means include a reset bumper 36 having a shank portion extending through and guided by an opening 37 formed in the main body member 11 along the thermostat centerline 32. The reset bumper is provided with a head portion 38 at its inner end adjacent to the mobile contact arm 24 which is engageable with a radial wall 39 in the main body member 1 1 to limit outward movement of the bumper.

Mounted on the outer end of the reset bumper 36 is a sleeve member 41 which is positioned over the outer end of the bumper and permanently connected thereto by a suitable adhesive such as an epoxy resin 42. The inner end of the sleeve member 41 provides an end surface 43 engageable with a mating surface 44 on the main body member 11 to limit inward movement of the reset bumper. Preferably, the sleeve member is formed with a sufficiently tight fit on the end of the reset bumper so that friction will retain these elements in a gauged position with respect to each other while the epoxy is applied and allowed to set. However, the adhesive 42 provides a permanent connection so that relative movement cannot occur between the sleeve and bumper after the adhesive sets.

The reset mechanism is assembled so that a slight clearance 46 exists between the inner end of the reset bumper and the adjacent portion of the mobile contact arm 24 when the two surfaces 43 and 44 are in engagement and the disc is in the reset position. However, movement of the disc to the operated position causes the mobile contact arm 24 to move into engagement with the end of the reset bumper and causes the reset bumper to move outwardly with respect to the body assembly to the condition of FIG. 3.

The head portion of the reset bumper 36 is formed with a curved generally spherical end face 46a so that it provides essentially a point contact with the adjacent surface of the mobile contact arm 24 with such contact occurring along the centerline 32. The location of the engagement of the bumper 31 with the mobile contact arm 24, however, is displaced laterally from the centerline in a direction toward the mobile contact 23. In the illustrated embodiment this is accomplished by providing an offset 47 in the mobile contact arm extending from the point 48, as best illustrated in FIG. 2a, to the free end of the contact arm. This offset insures that the location of the contact between the bumper 31 and the adjacent surface of the mobile contact arm will be displaced from the centerline at least an amount equal to the distance of the end of the offset 48 from the centerline 32. With this arrangement a lateral displacement of the location of the forces applied to the mobile contact arm 24 by the two bumpers 31 and 36 is insured even though the bumpers are symmetrical with respect to the centerline 32 and are movable therealong.

The various elements are arranged and proportioned so that when the reset bumper is pressed toward the disc to the limit of its travel as illustrated in FIG. 4, the disc 14 is pushed only past its position of instability adjacent to the operated position. The mobile contact am is not moved far enough to cause the two contacts to engage. Therefore, the switch remains open unless the disc snaps back to its reset position. If the reset is fully depressed and the disc remains at a temperature outside its reset temperature range, the disc will remain against the bumper 31 and will continue to produce a force F urging the bumper 31 toward the mobile contact arm. The force F, is spaced from the force F produced by the reset bumper 36 so a force couple is developed due to the opposed forces of the two bumpers 31 and 36 on the mobile contact arm. The force couple has a magnitude determined by the lateral spacing between the application of these forces and the amount of force of the disc on the bumper 31. Such force couple causes the mobile contact arm to bow slightly from its unstressed condition in a direction tending to maintain the contacts of the switch in their open, operated condition. Because of the step structure causing the force couple to be applied in the direction tending to retain the switch in its operated condition, there is no possibility for surface irregularities in either of the bumpers from causing an opposite directed force couple which could tend to close the switch even though the disc does not snap through to its reset position of stability. Consequently, the tolerances of manufacture need not be nearly as carefully controlled to prevent switch failure.

Because the travel of the reset bumper is mechanically limited by the engagement between the surfaces 43 and 44, excessive forces applied to the reset mechanism are not transmitted to the contact arm 24 so the contact arm cannot be damaged. The maximum force couple that can be applied to the mobile contact arm 24 is determined by the maximum force of the disc transmitted to the bumper 31 and the maximum radius of the bumper 31.

With the illustrated embodiment of this invention, the thermostat is trip-free in that it is impossible to lock the switch in the operated condition by blocking the reset mechanism in the extreme inward position. In fact, the thermostats operation is not adversely affected even if the reset mechanism is blocked in the extreme inward position since operation of the disc will cause the contacts to open whenever the disc reaches its main operating temperature.

Although a preferred embodiment of this invention is illustrated it is to be understood that various modifications and rearrangements of parts may be restored to without departing from the scope of the invention disclosed.

lclaim:

l. A trip-free manual reset thermostat comprising a body assembly, a switch providing a mobile contact arm supported in said body assembly, a snap disc in said body assembly movable with snap action between a reset position and an operated position in response to changes in temperature, operator means movable in said body assembly along an axis and operating to move said contact arm from a reset position to a switch-operated position in response to movement of said snap disc from its reset position to its operated position, reset means on said body assembly movable along said axis and operable to engage said contact arm and cause said operator means to move said disc from said operated position toward said reset position, interengageable stop surfaces on said body assembly and said reset means operable to prevent movement of said reset means toward said contact arm beyond a depressed position, said disc preventing reset means induced movement of said contact arm to its reset position when the temperature of said disc is outside a predetermined reset temperature range and said reset means is in said depressed position, said reset means and said operator means being symmetrical with respect to said axis, said contact arm, reset means and operator means being shaped so that the point of engagement between said contact arm and operator means is spaced along the length of said contact arm from the point of engagement between said contact arm and said operator means, said operator means and said reset means cooperating to apply a force couple to said contact arm resisting movement of said contact arm to its reset position when said reset is fully operated and said disc is at temperatures outside said predetermined reset temperature range.

2. A trip-free thermostat as set forth in claim 1 wherein said stop means prevent reset induced movement of said disc to said reset position.

3. A trip-free thermostat as set forth in claim 2 wherein said contact arm includes a resilient portion cantilever mounted on said body assembly for substantially pivotal movement about one end, and said force couple deflects said arm from its unstressed condition in a direction toward said operated position.

4. A trip-free thermostat as set forth in claim 3 wherein said contact arm is formed with an offset laterally spaced from said axis, and one of said points of engagement is on said offset.

5. A trip-free thermostat as set forth in claim 4 wherein the other of said points of engagement is on said axis.

6. A trip-free thermostat as set forth in claim 5 wherein said offset portion is spaced from said axis on the side thereof opposite said one end of said resilient portion, and said operator means engages said offset 7. A trip-free thermostat as set forth in claim 1 wherein said contact arm includes a resilient portion cantilever mounted on said body assembly for substantially pivotal movement about one end, and said force couple deflects said arm from its unstressed condition in a direction toward said operated position.

8. A trip-free thermostat as set forth in claim 7 wherein said contact is formed with an offset and one of said points of engagement is on said offset. 

1. A trip-free manual reset thermostat comprising a body assembly, a switch providing a mobile contact arm supported in said body assembly, a snap disc in said body assembly movable with snap action between a reset position and an operated position in response to changes in temperature, operator means movable in said body assembly along an axis and operating to move said contact arm from a reset position to a switch-operated position in response to movement of said snap disc from its reset position to its operated position, reset means on said body assembly movable along said axis and operable to engage said contact arm and cause said operator means to move said disc from said operated position toward said reset position, interengageable stop surfaces on said body assembly and said reset means operable to prevent movement of said reset means toward said contact arm beyond a depressed position, said disc preventing reset means induced movement of said contact arm to its reset position when the temperature of said disc is outside a predetermined reset temperature range and said reset means is in said depressed position, said reset means and said operator means being symmetrical with respect to said axis, said contact arm, reset means and operator means being shaped so that the point of engagement between said contact arm and operator means is spaced along the length of said contact arm from the point of engagement between said contact arm and said operator means, said operator means and said reset means cooperating to apply a force couple to said contact arm resisting movement of said contact arm to its reset position when said reset is fully operated and said disc is at temperatures outside said predetermined reset temperature range.
 2. A trip-free thermostat as set forth in claim 1 wherein said stop means prevent reset induced movement of said disc to said reset position.
 3. A trip-free thermostat as set forth in claim 2 wherein said contact arm includes a resilient portion cantilever mounted on said body assembly for substantially pivotal movement about one end, and said force couple deflects said arm from its unstressed condition in a direction toward said operated position.
 4. A trip-free thermostat as set forth in claim 3 wherein said contact arm is formed with an offset laterally spaced from said axis, and one of said points of engagement is on said offset.
 5. A trip-free thermostat as set forth in claim 4 wherein the other of said points of engagement is on said axis.
 6. A trip-free thermostat as set forth in claim 5 wherein said offset portion is spaced from said axis on the side thereof opposite said one end of said resilient portion, and said operator means engages said offset.
 7. A trip-free thermostat as set forth in claim 1 wherein said contact arm includes a resilient portion cantilever mounted on said body assembly for substantially pivotal movement about one end, and said force couple deflects said arm from its unstressed condition in a direction toward said operated position.
 8. A trip-free thermostat as set forth in claim 7 wherein said contact is formed with an offset and one of said points of engagement is on said offset. 